Dynasylan A is the ethyl ester of orthosilicic acid.
Dynasylan A is a colourless, low-viscosity liquid with SiO2 content of 28.5%. Use requires acid- or alkali-catalysed hydrolysis. Since all 4 ethoxy groups are able to participate in this reaction, Dynasylan A is regarded as tetrafunctional. Hydrolysis leads to silanol groups which, in a subsequent condensation reaction, form very stable siloxane bonds (-Si-O-Si-). Condensation starts before hydrolysis is complete. During storage of these hydrolysates condensation, continues until a gel is formed. The rate of gelation depends on the concentration of water.
In the Evonik literature it is frequently also referred to under the name TEOS (tetraethoxysilane).